Is there a saving throw to stop forced movement (a push, pull, or slide) from forcing you into a square that will damage you?

My wizard's tactic lately has been to try to Thunderwave enemies into the Wall of Fire. My DM gave the enemies a chance to save from entering the wall because it would cause them damage. I can't find anything under the forced movement section that says that except for "Catching yourself" which refers to the Falling section (PHB p 284) where it says

...if a power or bull rush forces you
over a precipice or into a pit, you
can immediately make a saving throw to
avoid going over the edge.

Did I miss the rule she's using? If there is no other rule, why is falling treated different? (i.e. what makes a character grab at the edge of the pit more effectively than at the edge of a wall of fire?)

Granted, she did apply the same rule when we were getting pushed around into a pool of acid a while ago, so either way she's applying it fairly.

2 Answers
2

Blocking Terrain: Forced movement
can’t move a creature through blocking
terrain (page 61). Every square along
the path must be a space the creature
could normally occupy.

Challenging Terrain: Forced movement
can make some powers more effective or
hinder them, depending on the specific
challenging terrain. The DM can
require the target of forced movement
to make a check as if it were moving
voluntarily across the terrain, with
the same consequence for failure.

Hindering Terrain: Forced movement can
force targets into hindering terrain.
Targets forced into hindering terrain
receive a saving throw immediately
before entering the unsafe square they
are forced into. Success leaves the
target prone at the edge of the square
before entering the unsafe square. If
the power that forced the target to
move allows the creature that used the
power to follow the target into the
square that the target would have
left, the creature can’t enter the
square where the target has fallen
prone. If forced movement pushes a
Large or larger creature over an edge,
the creature doesn’t fall until its
entire space is over the edge. On the
creature’s next turn, it must either
move to a space it can occupy or use a
move action to squeeze into the
smaller space at the edge of the
precipice.

A DM can allow a power that pushes a
target more than 1 square to carry the
target completely over hindering
terrain.

Here is a good summary of some recent answers from WoTC Customer service. It is still an open question if you can cause a target to take damage multiple times by sliding them in and out of a zone. (Obviously thunder wave can't be used this way, but other abilities can).